What Is the Low FODMAP Diet?

If you and your practitioner are working on a plan for gastrointestinal (GI) health, you likely have heard about the low FODMAP diet. But what exactly are FODMAPs, what do they do, and what are the pros and cons of being on a low FODMAP diet?

What are FODMAPs?

FODMAPS are sugars (carbohydrates) that are not easily absorbed but are easily fermented by the bacteria in our guts. Technically, FODMAP stands for: Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols.

Fermentable

Fermentation is the process that occurs within the bacterial cells in our guts. It’s an enzymatic process that causes carbohydrates to be converted to gases.

Oligosaccharides

These are polymers (long chains) of monosaccharides such as glucose, galactose (galactooligosaccharides), and fructose (fructans) typically found in foods such as wheat, rye, onions, garlic, and legumes.

Disaccharides

As the name implies, disaccharides result from the joining together of two monosaccharide groups. A good example of a disaccharide is the lactose (glucose + galactose) found in dairy products such as milk, cheese, and yogurt.

Monosaccharides

These are the building blocks of disaccharides and oligosaccharides. Fructose is a disaccharide found in honey and apples as well as high-fructose corn syrup.

Polyols

These are sugar alcohols formed by the hydrogenation (addition of hydrogen) to a sugar. For example, sorbitol is the polyol formed by the addition of an extra hydrogen to glucose. Sugar alcohols (mannitol is another example) are commonly used as sweeteners.

What do FODMAPs do in the body?

Normally, FODMAPs are digested to their smallest parts, the monosaccharides (e.g. glucose), which are then used as fuel for the cells of the body. However, when we are unable to effectively digest (e.g. lactose intolerance) and absorb these sugars, they become available to be fermented by gut bacteria and contribute to osmotic load. When bacteria ferment FODMAPs, the sugars get converted into a variety of different compounds, known as metabolites. Among the metabolites produced are gases such as carbon dioxide, methane, and hydrogen. These gases contribute to feelings of bloating and flatulence. Increased osmotic load occurs because these sugars are water soluble and attract and retain water in the gastrointestinal tract, which in turn may contribute to increased frequency of bowel movements.

What are the benefits of a low FODMAP diet?

The low FODMAP diet was originally hypothesized by scientists at Monash University in Australia.1,2 The thinking was that by limiting FODMAP intake, one could effectively starve the gut bacteria that produce gases. An elimination phase should be followed by a period of reintroduction to determine which FODMAPs are tolerable to the individual.

Since the first introduction of the low FODMAP diet, it has been extensively studied. The results are mixed but generally positive.3,4 The efficacy of the elimination phase of the diet has been reported to be as low as 15%3 and as high as 86%,4 with subjects reporting a clinically meaningful reduction in gastrointestinal complaints. Fewer studies have been conducted on the reintroduction phase of the FODMAP diet, and approaches and results vary widely.

What are the downsides of a low FODMAP diet?

A low FODMAP diet calls for the complete elimination of many foods including wheat; barley; rye; all legumes; vegetables such as asparagus, cauliflower, and onions; fruits such as apples, pears, mangoes, peaches, and grapes; and all dairy. Such a restricted dietary intake may increase the risk for gaps in nutrients such as calcium, zinc, and folate.5

In addition to micronutrient deficiencies, the dietary elimination of FODMAP containing foods may result in a decreased intake of fiber.5 Fiber contains carbohydrates, which act as prebiotics (food for beneficial microbes).

In summary

The low FODMAP diet may provide a useful short-term tool for clinicians; however, patients should work closely with their healthcare provider to determine a multimodal approach to managing GI health long term. For more information on low FODMAP diets, lists of foods to eat and foods to avoid, and a useful FODMAP app, consider visiting the webpage maintained by the Monash university team and discussing with your healthcare practitioner.6

About Nikky Contractor, PhD; Metagenics Senior Director for Nutritional Science and head of R&D

Dr. Contractor earned her PhD in Immunology from the University of Pennsylvania, where she studied the role of gut microbiota in models of inflammation and the function of the intestinal immune system. She continued these research interests as a postdoctoral research fellow at the National Institutes of Health in Bethesda, MD. Dr. Contractor has extensive experience running research programs in both academic and industry research settings across the spectrum of preclinical to clinical research with over 10 years of experience in the development of nutritional products. She has held leadership positions at Wyeth, Pfizer and Nestle. She has authored over 15 peer-reviewed publications. Dr. Contractor is passionate about the development of innovative, scientifically supported new products to meet the health goals of individuals.